Therefore, those people I referred to who continually perform their prayers with tayammum (dry ablution) while having no legitimate excuse— their prayers are invalid for the entire period during which they do this. A Muslim must fear Allah and fulfil what Allah has made obligatory in the prescribed manner.

Tayammum is merely a concession in situations of real need; it is a substitute for water. Thus, when water is available and one is able to use it, dry ablution is not valid. Allah knows best.